This invention relates to machinery subject to torque loads and, specifically, to a mounting assembly that reduces or eliminates torque roll associated with soft, passive machinery mounts.
There are many pieces of machinery that are subject to torque loads which cause misalignment between machinery components, and/or require couplings with misalignment capability. At high speeds, rotating elements of machinery can apply high torque loads to mounts for the machinery, these torque loads typically referred to as causing xe2x80x9ctorque rollxe2x80x9d, an undesirable situation. The normal manner to accommodate torque roll is simply to provide expensive and space-consuming line shaft couplings which accommodate misalignment in machinery components due to torque roll caused by high torque forces.
Current submarine designs use hard mounting of the main propulsion components to minimize misalignment due to high torque loads. Unfortunately, this approach provides a direct unattenuated path for noise transmission and is a serious drawback to extremely quiet operation.
Advanced submarine designs use elastomeric mounts to provide noise isolation between the propulsion machinery and rest of the structure. At high speeds the overturning moment from the high line shaft torque can cause one side of the machinery to lift. This places the elastomeric isolators on one side in tension, a design condition that is not allowed. In addition, the misalignment at high torque forces the use of the expensive and space consuming line shaft coupling mentioned above.
That is, current practice uses the weight of the main propulsion unit [MPU] to keep the lifting side mounts in compression. However, for advanced submarines, reduced MPU weight and narrower athwartship mounting locations can cause the mounts to unload. Regular elastomeric mounts have been proposed to be used on one side in an over/under configuration with the xe2x80x9coverxe2x80x9d mounts in compression under torque roll. Used in this fashion they have to be pre-compressed so that the under mounts do not unload during high torque loads. This pre-compression will cause the permanent deformation, due to creep, to occur earlier and shorten service life. Additionally, the low speed noise isolation will be reduced as the addition of the upper mounts will increase the mount spring constant and cause the basic system resonance frequency to increase and thereby reduce the frequency difference between the noise stimuli and the basic system resonance. This will also reduce the noise isolation attenuation with respect to an xe2x80x9call underxe2x80x9d mount configuration.
According to the present invention, a mounting assembly is provided which significantly reduces or substantially eliminates torque roll of soft passive mounts for machinery (such as elastomeric isolation units), without compromising the isolation performance or the service life of the mounts. The invention achieves this advantage in a simple yet effective manner but can be used in a wide variety of different ways, with different equipment, to get desired results over extended periods of time. While applicable to a wide variety of machinery, the invention is particularly suitable for use in marine applications, such as in submarines.
According to one aspect of the present invention there is provided a mounting assembly for a device subject to a torque roll force in a generally upward first direction on a first side of the device, and a torque roll force in a generally downward second direction on a second side of the device, comprising: At least one soft passive mount for the device on each of the first and second sides, below and operatively engaging at least a portion of the device; and a first inflatable element disposed at or adjacent the first side of the device and resisting movement of the device in response to the torque roll force in the first direction.
Preferably the first inflatable element provides a counter-force to the torque roll force in the first direction substantially proportional to the torque roll force in the first direction. For example, the first inflatable element may comprise at least one airbag operatively connected to a source of compressed gas. The assembly may further comprise means for adjusting the pressure of gas in the at least one airbag in response to the level of the torque roll force in the first direction. Typically, the first inflatable element is mounted between a substantially stationary support element and an upper surface of a portion of the device to apply a substantially downwardly directed force to the device counter to the torque roll force in the first direction.
The invention also preferably further comprises a second inflatable element operatively engaging the device at or adjacent the second side thereof and resisting movement of the device in response to the torque roll force in the second direction. Desirably the second inflatable element provides a counter-force to the torque roll force in the second direction substantially proportional to the torque roll force in the second direction. For example, the second inflatable element may also comprise at least one airbag operatively connected to a source of compressed gas, and the assembly may further comprise means for adjusting the pressure of gas in the at least one airbag in response to the level of the torque roll force in the second direction. Typically, the second inflatable element is mounted below a portion of the device at the second end of the device. A wide variety of conventional soft passive mounts may be utilized, such as elastomeric isolation mounts. Also the device may comprise a wide variety of different types of equipment or machinery, such as a propulsion unit or a component of a propulsion unit. By practicing the invention, typically a rotatable shaft connected to the propulsion unit, or component of the propulsion unit, can be connected to another unit without expensive and space-consuming conventional line shaft couplings described above. The invention is particularly applicable where the propulsion unit or component of the propulsion unit [such as an MPU or gearing for an MPU] is a marine unit for driving a propeller, such as a submarine propeller.
According to another aspect of the present invention an assembly is provided comprising: A device having first and second sides having first and second mounting elements. At least one soft passive mount for the device below and operatively engaging each of the first and second mounting elements. A first inflatable element mounted between a substantially stationary support element and an upper surface of the first mounting element, and when inflated applying a substantially downward force on the first mounting element. And a second inflatable element operatively engaging the second mounting element below the second mounting element, and when inflated applying a substantially upward force on the first mounting element.
Typically, each of the inflatable elements is operatively connected to a source of compressed gas, and applies a force substantially proportional to an opposite force applied thereto. The device, and the passive mounts, etc., may be as described above, with the first side of the device to starboard and the second side to port.
According to another aspect of the present invention there is provided a method of reducing or substantially eliminating torque roll of a propulsion element, having first and second sides mounted by soft passive mounts, wherein the element is subject to a torque roll force in a generally upward first direction on the first side of the element, and a torque roll force in a generally downward second direction on the second side of the element, the method utilizing at least one inflatable element, and comprising: a) Directly or indirectly sensing the torque roll force in at least one of the first and second directions. And b) in response to a), controlling the pressure of gas in the at least one inflatable element to resist at least one of the torque roll forces in the first and second directions.
Preferably the method as described above utilizes first and second inflatable elements mounted at or adjacent each of the first and second sides of the propulsion element, and a) and b) are practiced to resist torque roll forces in both the first and second directions. Also, preferably b) is practiced to provide resistive forces substantially proportional to the torque forces in both the first and second directions. For example, the propulsion element may be a marine propulsion element operatively connected to a propeller, and the method may further comprise c) driving the propeller, including at least in part with the propulsion element, to power a marine vessel containing the propulsion element.